The excellent mechanical properties of polyurethanes have led to their frequent use in blood-contacting applications. To prevent platelet adhesion, it is often necessary to employ anti-thrombotics. The goal of this project is to develop a diffusional barrier film for polyurethanes which will control the release of echistatin, a recently-discovered anti-thrombotic, at the surface of the coated polyurethanes. The potency of echistatin, combined with the zero-order release kinetics controlled by the barrier film, will inhibit platelet adhesion while minimizing the bleeding risks associated with other anti-thrombotics.